Pneumatic conveyance system

ABSTRACT

A pneumatic conveyance system for unloading a dry flow railroad hopper car. A centrifugal blower draws suction on a cyclone separator disposed adjacent the unloading point. Solids separated in the separator are entrained in an air stream provided by a positive displacement pump such as a Root&#39;&#39;s pump and are pneumatically conveyed to the delivery point. The centrifugal blower and positive displacement pump are driven by the same motor so that the air rate-power characteristics of the centrifugal blower and positive displacement pump counteract each other.

United States Patent 1 Feder 1 Jan. 9, 1973 [54] PNEUMATIC CONVEYANCE SYSTEM Primary Examiner-Harvey C. Hornsby Assistant Examiner-Hadd S. Lane 75 I t r: Fri dhelm R. Feder Mem his, I 1 men 0 Tel? p Attorney-Ralph D. Dinklage et al.

[73] Assignee: Wedco, Inc., Bloomsbury, NJ. 57] ABSTRACT Filed: July 1971 A pneumatic conveyance system for unloading a dry [21] APPL N03 v164,55 flow railroad hopper car. A centrifugal blower draws suction on a cyclone separator disposed adjacent the unloading point. Solids separated in the separator are [52] U.S. Cl ..302/13 entrained in an air stream provided by a positive [221;] g t.l 51340 11 placement pump Such as a Roofs pump and are pnew 1 0 matically conveyed to the delivery point. The centrifugal blower and positive displacement pump are driven [56] References Cited by the same motor so that the air rate-power charac- UNITED STATES PATENTS teristics of the centrifugal blower and positive dis- 727 030 5/1903 T1 h 302/12 S placement pump counteract each other.

, 1g man AIR FILTER I I5 20 Claims, 1 Drawing Figure RAlLROAD DRY FLOW HOPPER CAR- Iz I4 [3 I6 23 IO II AIR FILTER v Roo'rs 4 CENTRIFUGAL 17 TYPE BLOWER PUMP sro. 6" LINE 4:? L (5 24 PNEUMATIC CONVEYANCE SYSTEM BACKGROUND This invention relates to pneumatic conveying particles and provides a system for that service. The new system has been found particularly effective for unloading of pellets of plastics, e.g., polyethylene, polypropylene, etc., from railroad hopper cars.

Several pneumatic unloading systems are known, prominent systems being the following.

1. Negative System Using Single Stage Centrifugal Blower This type of system is used to convey material from a hopper car to a fixed point. The system comprises a line leading from the unloading point at the hopper car to the delivery point where the line connects with a cyclone separator outfitted with a rotary gate valve. The end of the line at the unloading point is open for taking in air, and a centrifugal blower draws suction on the separator. The system is extremely simple and easy to maintain. Though a filter may be installed at the air intake, a filter is not required between the separator and blower to protect the blower, since a centrifugal blower can without harm pass particles and dust. Safety valves are not required, since a centrifugal blower operates virtually at a constant pressure regardless of loading. This system is suitable for short distances and relatively low capacity. Since the blower can only develop pressure of about 1 psi or 2 inches of mercury vacuum, material to air ratio is low and pipe sizes large. The system is sensitive to loading. Run at under capacity (i.e., low solids content in the air), the conveying velocity and the power consumption increase. The system cannot recover from short overloads, since a line restriction will not cause the blower to overload and develop a higher pressure. Properly designed clean out ports, however, make it possible to restart a choked up system, easily and without waste of material. See U.S. Pat. No. 2,374,584, Cannon (1945).

2. Negative System Using Positive Displacement Pump The system is generally set up as the system No. 1, above, except that a positive displacement pump is used instead of a centrifugal blower. This commonly requires an efficient air filter between the cyclone and the pump, since the pump cannot satisfactorily pass some kinds of solids, e.g., plastics. Also a vacuum relief valve in the pump intake line may be necessary. Positive displacement pumps, e.g., a Roots blower, i.e., a pump having two interengaging, two lobed impellers, can, depending on design, develop psi (or inches of mercury vacuum) or more. Therefore, a system using a positive displacement pump can operate at high material to air ratios (pounds of material to pounds of air). This means lower air volumes and smaller pipe sizes. The system performs well at loading less than maximum, and generally, for short periods of time at high power consumption, the pump can develop pressure or suction peaks far in excess of those permissible for continuous operation. This fact allows the system to cope with occasional overloads of short duration. It also accommodates variations in the system. The vacuum relief valve is provided to prevent line stoppage from resulting in a vacuum which would cause collapse of equipment.

The separator can be outfitted with a rotary gate or a flapper gate which is held closed due to the pressure difference between the system and the atmosphere. Where a flapper gate is used, the pump is, at preset time intervals, turned off to allow the receiver to empty. Since the system is always turned off under load leaving material in the line, it has to be operated at less capacity than a continuous system of similar size to provide a power margin for start up. For short conveying distances, however, the ability of most positive pressure pumps to supply high pressure peaks is generally sufficient to start air and material moving. 3. Positive Systems In this type of operation a positive displacement pump delivers air to the inlet of the conveying conduit at the unloading point. These systems are generally used to move material from a fixed point to a receiving point which may be varied. Positive systems are preferable if either negative or positive can be used, since due to the higher air viscosity a positive system can be used for higher material to air ratios and longer distances than a negative system. A positive system, however, is in appropriate for unloading dry flow hopper cars which are the particular concern here. Systems as described but employing a centrifugal blower instead of a positive displacement pump have been proposed. See U.S. Pat. No. 2,814,531, Murray (1957); U.S. Pat. No. 3,155,431, Baldwin (1964); and U.S. Pat. No. 3,236,565, Kester (1966), which also employs a centrifugal blower as in No. 1, above. 4. Negative, Positive System Using Centrifugal Blower The simplest form of a negative, positive system is a set up utilizing a centrifugal blower in the conveying line between the unloading point and the cyclone separator. The performance characteristic of this type of system is similar to No. 1. See U.S. Pat. No. 1,468,966, Harrington (1923). 5. Negative Positive System Using Positive Displacement Pump In this set up material is sucked from the hopper car into a cyclone separator disposed at the unloading station and drops through an air lock into a positive pressure line leading to a cyclone separator at the delivery point. Suction and positive pressure are provided by a positive displacement pump in a line connecting the first cyclone separator air outlet with the outlet side of the airlock of that separator. This system has performance characteristics similar to No. 2, having similar requirements with respect to a filter and relief valves. It is generally used for medium and high capacities (from 3 tons per hour up). Since it is desirable to keep the distance of negative conveying short, negative, positive systems are often built as portable units, which allows the placing of the unit next to the railroad hopper car to be unloaded. See U.S. Pat. No. 2,230,425, Finnegan (1941 U.S. Pat. No. 2,946,626, Atkinson (1960).

THE INVENTION The pneumatic conveyance system of the invention comprises a separator, e.g., a cyclone separator, disposed adjacent the unloading point, and communicated with the unloading point for receiving an airsolids mixture therefrom. An air blower, e.g., centrifugal blower, draws suction on the separator and provides the air for the conveyance. Solids separated in the separator are discharged therefrom through an air lock disposed in the bottom of the separator, into an air stream provided by a positive displacement air pump, e.g., a Roots type pump. The air stream entrains the solids and pneumatically conveys them to the delivery point.

The air blower and the air pump are driven by the same drive, e.g., a single motor drives the two machines. Thereby the air load-power operating characteristics of the machines are counterbalanced. The air blower, which operates at a pressure differential which is substantially constant for varying air throughput, draws more power as the air throughput (SCF) increases. The air throughput increases as solid material conveyed decreases. Thus, for the air blower, as load, in terms of solid material conveyed, increases, the power consumption decreases.

The power-load characteristic of the positive displacement pump is the opposite. Thus, for it, as load, in terms of solid material conveyed, increases, the power consumption increases.

By placing the two air moving machines in a common drive, the respective operating characteristics are counterbalanced, to the benefit of operation of both machines. If the load drops to no load, i.e., no solid material being conveyed, the air blower power consumption is high. For that operating condition, the power consumption of the positive displacement pump is low. Therefore, by using a common drive, operation is improved, in particular, overloading of the motor drive means is prevented.

THE DRAWING An embodiment of the invention is depicted in the accompanying flow diagram.

A dry flow railroad hopper car 1 is parked on a railroad siding 5 as the unloading point. The car can contain, e.g., polypropylene pellets of size one-sixteenth to one-eighth inch. The car 1 is outfitted with standard size 6 inch discharge pipe 3 provided for unloading of the car by pneumatic conveyance of the solid material. For that conveyance, air is drawn from the atmosphere into one end of the pipe 3, through an air filter 4. Suction is applied to the other end of the pipe 3. As a safety precaution, to prevent drawing a vacuum on the car 1 which would damage, e.g., collapse, the car, the hatch 2 is left open during emptying of the car.

A conventional cyclone separator 7 is positioned adjacent the siding 5. Separator 7 has an inlet 9 for the mixture of air and solids; a separated air outlet 8 for separated air; a separated solids outlet 10 for separated solids; and an air lock feeder valve 10, e.g., a star feeder, for metering discharge of solids from the separator.

The separator inlet 9 is communicated with the hopper car discharge pipe 3 by a pipe 6 which can be, and this is an advantage of the apparatus of the invention, a 6 inch pipe, i.e., the same line size as that of the hopper car discharge pipe 3, which as mentioned, is a standard size on hopper cars, in particular, a 6 inch line. inlet 9 is a standard 6 inch inlet. 7

The separated air outlet 8 is communicated with the inlet of a centrifugal air blower 11, which discharges separated conveying air to the atmosphere via pipe 12. Pipe 8a leads from the separator to the air blower 11, and can, and preferably is, also a 6 inch pipe. Outlet 8 is a standard 6 inch outlet.

A Roots type air pump 16, outfitted with air intake pipe 14 having air filter 15, draws air from the atmosphere and pumps the air into line 17 which leads to junction 19 where the air entrains solids discharge from the separator. The resulting air-solids mixture enters line 20 which leads to delivery point for the solids. A pressure differential gage 18 measures the pressure differential of the air pump 16 and is connected in a control system (not shown) so that if the pressure dif-- ference exceeds a selected value, the air pump is turned off, as is also the air blower 11, by stopping of the motor 13.

A second cyclone separator 21 is disposed at the delivery point. Separated air is vented to the atmosphere via line 22; separated solids pass through air lock 23 into silo 24.

As described above, a feature of the invention is the use of common drive for the air blower and the air pump. Thus air blower 11 and air pump 16 are driven by motor 13, which can be and preferably is, a constant RPM electric motor drive.

ADDENDA The air blower, 11 in the drawing, draws suction in the separator 7 for conveyance of the solids pneumatically from the car 1 to the separator. Since the interconnecting lines are under suction, large line sizes are called for. In general a 6 inch line is well suited for theservice, and that line size offers the further advantage, noted above, that it matches the line size of the hopper car discharge pipe 3.

Line 20, communicating the station at which separator 7 is located, which is adjacent the railroad siding 5, and the delivery point, which is remote from the siding, is a pressure line, i.e., the air therein is at above atmospheric pressure. Also, commonly, it is a long line. Since it is a pressure line, it can be of small size, which is an advantage from a cost point, in view of its length. Thus line 20 can be a pipe of a pipe size less than 6 inches, e.g., 4 inches or 3 inches, or smaller.

The air blower 11, in the described embodiment is a centrifugal blower. It can be a blower characterized in that it passes remnant solids contained in the separated air stream in line 8a, without interference in the operation of the blower. A centrifugal blower meets that requirement. A positive displacement pump, however, does not. In such a pump, the solids interfere with the surfaces in sliding contact, which surfaces are exten-' sive. Plastics which are pliable or thermoplastic may be smeared over those surfaces clogging the machine. Were a positive displacement pump used for the service, it would be necessary to install a filter, and an efficient and therefore expensive one, in line 8a. According to the invention the air from separator 7 can be conveyed to the air blower without filtration.

A further advantage of the air blower is that the suction pressure is low, i.e., little suction, so that only a slight vacuum is drawn on the hopper car. Thus the likelihood of collapsing the car is reduced. That is an important consideration as in the art, collapse of the cars sometimes occurs.

Another advantage of the system employing the air blower is that a relief valve for the air blower operation is not required.

The air blower 15 can be a centrifugal blower as is described in Bulletin CTR-106, Chicago Turbo Pressure Blowers Design 15, Chicago Blower Corp., Franklin Park, Ill. Such machines have the described characteristic for the air blowers used herein. Power consumption increases with an increase in air throughput, which means that where, as here, the air is used for pneumatic conveyance, since as solids conveyed increases, air throughput decreases, as solids conveyed decreases, power consumption increases. Such machines operate at a substantially constant pressure differential with varying air throughput in SCF/min.

The positive displacement air pump, e.g., the Roots type blower 16, is a variable output pressure machines, delivering a substantially constant volume for a constant RPM, and power consumption of the machine increases with increasing load, i.e., the power-load characteristic is the opposite of that of the air blower, e.g., centrifugal blower 11. The characteristics of the positive air displacement pump are such as is disclosed in Model 4509, Air Pump Performance Curves, Schwitzer Corp., Indianapolis, Ind.

The system of the invention is well suited for capacities of up to 20 tons per hour of plastic pellets, e.g., polypropylene, of H16 )4; inch size. Larger size particles can be conveyed, e.g., up to one-fourth inch. The system is comparable in cost with systems of conventional design of lower capacity, e.g., 5 tons per hour. A tons per hour system, according to the invention, for the material mentioned, can employ a 40 horsepower, 3,600 RPM motor.

When conveying pellets of sizes such as mentioned, the line 20 can be connected directly to the silo 24. Separator 21 is not then required. In this case, the silo should be vented.

In the illustrated embodiment, the conveying of material which is principilly coarser than 100 mesh is contemplated. For conveying finer material, the discharge 12 of blower 11 can be communicated with the inlet end of the hopper car pipe 3. Line 3 could be sealed at the flange on which the air filter 4 is mounted, but a small adjustable vent should be placed in the recycle line. The flow rate from the car can then be adjusted by means of the adjustable vent. See my copending application Ser. No. 33,468 filed Apr. 30, 1970.

What is claimed is:

1. Apparatus for pneumatic conveyance of material comprising:

a. a separator having an inlet for receiving an airsolids mixture for conveyance by the apparatus and for separation thereof into a separated air stream and separated solids, said separator having an air outlet for the separator air and a solids outlet for the separated solids,

b. an air blower having an inlet communicated with the separator air outlet for drawing suction on the separator and separator inlet for pneumatic conveyance to the separator, said air blower passing remnant solids contained in the separated air stream without interference with the operation thereof and being characterized by increase in power consumption with increase in air throughput,

c. a positive displacement air pump and conduit means communicating the discharge of the positive displacement air pump with the solids outlet of the separator for take up and pneumatic conveyance of the separated solids to delivery point therefor, and

d. a common drive for the air blower and the positive displacement air pump.

2. Apparatus according to claim 1, said air blower having a constant pressure differential.

3. Apparatus according to claim 1, said air blower being a centrifugal blower.

4. Apparatus according to claim 1, said separator being a cyclone separator, said communication of the separator air outlet and the inlet of the blower being a conduit for delivering the separator air to the air blower without filtration.

5. Apparatus according to claim 1, and an inlet pipe for conveyance of air-solids mixture from an unloading point for the solids to the separator, said inlet pipe being a 6 inch pipe.

6. Apparatus according to claim 5, and a delivery pipe for said pneumatic conveyance to the delivery point, said delivery pipe being of a pipe size less than 6 inches.

7. Apparatus according to claim 1, said air blower being a centrifugal blower, said separator being a cyclone separator, said communication of the separator air outlet and the inlet of the air blower being a conduit for delivering the separator air to the air blower without filtration.

8. Apparatus according to claim 7, and an inlet pipe for conveyance of air solids mixture from an unloading point for the solids to the separator, said inlet pipe being a 6 inch pipe.

9. Apparatus according to claim 8, and a delivery pipe for said pneumatic conveyance to the delivery point, said delivery pipe being of a pipe size less than 6 inches.

10. Apparatus according to claim 1, and a second separator, said second separator being disposed at said delivery point, and a delivery pipe for said pneumatic conveyance to the delivery point and communicating with the second separator.

11. Apparatus according to claim 7, and a second separator, said separator being disposed at said delivery point, and a delivery pipe for said pneumatic conveyance to the delivery point and communicating with the second separator.

12. Apparatus according to claim 11, and an inlet pipe for conveyance of air-solids mixture from an unloading point for the solids to the first mentioned separator, said inlet pipe being a 6 inch pipe.

13. Apparatus according to claim 12, said delivery pipe being of a pipe size less than 6 inches.

14. A plant for unloading material from a dry flow railroad hopper car and delivering the material to a remote delivery point, comprising:

a. a railroad siding for parking the car during unloading,

b. apparatus according to claim 1 disposed adjacent the siding,

c. an inlet pipe for pneumatic conveyance of the material from the car to said separator,

d. a second separator, said second separator being disposed at the delivery point, and

e. a delivery pipe for said pneumatic conveyance to the delivery point and communicating with the second separator.

being of a pipe size less than 6 inches.

15. Plant according to claim 14, said air blower being a centrifugal blower, said first mentioned separator being a cyclone separator, said communication of the separator air outlet and the inlet of the air blower being a conduit for delivering the separator air to the air blower without filtration.

16. Plant according to claim 15, said inlet pipe being a 6 inch pipe.

17. Plant according to claim 16, said delivery pipe l0 18. Process of unloading material from a dry flow railroad hopper car and delivering the material to a remote delivery point, which comprises:

pneumatically conveying the material from the car to a cyclone separator disposed adjacent the car by communicating the car and separator for the pneumatic conveyance and drawing suction on the separator with an air blower passing remnant solids contained in the separated air stream without interference with the operation thereof and being characterized by increase in power consumption with an increase in air throughput, b. separating the material from the conveying air in the separator,

c. discharging the separated solids from the separa pumping an air stream into the discharged solids said air pump with a 

1. Apparatus for pneumatic conveyance of material comprising: a. a separator having an inlet for receiving an air-solids mixture for conveyance by the apparatus and for separation thereof into a separated air stream and separated solids, said separator having an air outlet for the separator air and a solids outlet for the separated solids, b. an air blower having an inlet communicated with the separator air outlet for drawing suction on the separator and separator inlet for pneumatic conveyance to the separator, said air blower passing remnant solids contained in the separated air stream without interference with the operation thereof and being characterized by increase in power consumption with increase in air throughput, c. a positive displacement air pump and conduit means communicating the discharge of the positive displacement air pump with the solids outlet of the separator for take up and pneumatic conveyance of the separated solids to delivery point therefor, and d. a common drive for the air blower and the positive displacement air pump.
 2. Apparatus according to claim 1, said air blower having a constant pressure differential.
 3. Apparatus according to claim 1, said air blower being a centrifugal blower.
 4. Apparatus according to claim 1, said separator being a cyclone separator, said communication of the separator air outlet and the inlet of the blower being a conduit for delivering the separator air to the air blower without filtration.
 5. Apparatus according to claim 1, and an inlet pipe for conveyance of air-solids mixture from an unloading point for the solids to the separator, said inlet pipe being a 6 inch pipe.
 6. Apparatus according to claim 5, and a delivery pipe for said pneumatic conveyance to the delivery point, said delivery pipe being of a pipe size less than 6 inches.
 7. Apparatus according to claim 1, said air blower being a centrifugal blower, said separator being a cyclone separator, said communication of the separator air outlet and the inlet of the air blower being a conduit for delivering the separator air to the air blower without filtration.
 8. Apparatus according to claim 7, and an inlet pipe for conveyance of air solids mixture from an unloading point for the solids to the separator, said inlet pipe being a 6 inch pipe.
 9. Apparatus according to claim 8, and a delivery pipe for said pneumatic conveyance to the delivery point, said delivery pipe being of a pipe size less than 6 inches.
 10. Apparatus according to claim 1, and a second separator, said second separator being disposed at said delivery point, and a delivery pipe for said pneumatic conveyance to the delivery point and communicating with the second separator.
 11. Apparatus according to claim 7, and a second separator, said separator being disposed at said delivery point, and a delivery pipe for said pneumatic conveyance to the delivery point and communicating with the second separator.
 12. Apparatus according to claim 11, and an inlet pipe for conveyance of air-solids mixture from an unloading point for the solids to the first mentioned separator, said iNlet pipe being a 6 inch pipe.
 13. Apparatus according to claim 12, said delivery pipe being of a pipe size less than 6 inches.
 14. A plant for unloading material from a dry flow railroad hopper car and delivering the material to a remote delivery point, comprising: a. a railroad siding for parking the car during unloading, b. apparatus according to claim 1 disposed adjacent the siding, c. an inlet pipe for pneumatic conveyance of the material from the car to said separator, d. a second separator, said second separator being disposed at the delivery point, and e. a delivery pipe for said pneumatic conveyance to the delivery point and communicating with the second separator.
 15. Plant according to claim 14, said air blower being a centrifugal blower, said first mentioned separator being a cyclone separator, said communication of the separator air outlet and the inlet of the air blower being a conduit for delivering the separator air to the air blower without filtration.
 16. Plant according to claim 15, said inlet pipe being a 6 inch pipe.
 17. Plant according to claim 16, said delivery pipe being of a pipe size less than 6 inches.
 18. Process of unloading material from a dry flow railroad hopper car and delivering the material to a remote delivery point, which comprises: a. pneumatically conveying the material from the car to a cyclone separator disposed adjacent the car by communicating the car and separator for the pneumatic conveyance and drawing suction on the separator with an air blower passing remnant solids contained in the separated air stream without interference with the operation thereof and being characterized by increase in power consumption with an increase in air throughput, b. separating the material from the conveying air in the separator, c. discharging the separated solids from the separator, d. pumping an air stream into the discharged solids with a positive displacement air pump and thereby pneumatically entraining the discharged solids, and e. driving said air blower and said air pump with a common drive, f. conveying the pneumatically entrained solids to the delivery point.
 19. Process according to claim 18, said air blower being a centrifugal blower.
 20. Process according to claim 19, said separator being communicated with the air blower by a conduit for delivery of air from the separator to the air blower without filtration. 